In a manufacture process of a semiconductor device or an LCD, a resist film forming process is photolithographically performed on a substrate to be processed. During such process, a mask substrate having a predetermined pattern lithographed thereon is employed in exposing the substrate to be processed. In order to lithographically form the mask pattern on the surface of the mask substrate, a series of steps are taken: first, a resist is spin coated on the mask substrate made of, e.g., glass, to thereby form a resist film; and then the resist film is exposed and developed, to thereby obtain a desired pattern.
During the spin coating, the substrate G is rotated so that a helical air flow pattern is generated on a surface of the substrate G, to thereby rapidly remove solvent (thinner) ambient from the surface of the substrate G, which in turn facilitates evaporation of the solvent from the coating solution. However, at a portion of the substrate G where a rapid evaporation of the solvent takes place, the processing solution from nearby gets attracted thereto by the surface tension thereof, and as a result, such portion of the substrate G tends to have a greater thickness than that of other portions. In order to resolve such problem, it is desirable that the evaporation rate of the solvent on the surface of the substrate G is uniformly adjusted.
However, in a case of using a polygonal substrate G, as shown in FIG. 1A, peripheral sides of the substrate G rotate cutting through an outer ambient (ambient with low solvent concentration), which in turn facilitates the evaporation taking place at such peripheral sides of the substrate G. As a result, not only a greatest thickness is obtained at the corners of the substrate G, but also a thickness profile slanted towards corners in one direction is obtained at the peripheral sides thereof, as shown in FIG. 1B. These features greatly contribute to a deterioration of thickness profile of the substrate G.
Disclosed in Japanese Patent Laid-open Publication No. 2000-271524 is a spin chuck including a circular plate provided with a depressed portion, i.e., a square recess, in which a substrate is placed, to prevent the ambient from coming into contact with the substrate, and in addition, a method for controlling the air flow pattern upon rotation. Moreover, there is disclosed in Japanese Patent Laid-open Publication No. H8-131929 a method for controlling air flow for a non-polygonal substrate by installing a ring member around a peripheral portion of a semiconductor wafer.
In order to form a pattern with a uniform line width with respect to the mask substrate, there is necessary to secure an in-surface uniformity of a thin film resist layer. However, the conventional spin chuck cannot sufficiently suppress an increase in thickness at the corner portions of the polygonal substrate. An air flow that is produced at a surface of the substrate G during a rotation thereof is considered as a contributing factor in such feature. Accordingly, there is a need to examine a way to adequately control the air flow that occurs at the substrate G.
In addition, with a conventional spin chuck 100, a loading/unloading process of a substrate G is somewhat complicated. Namely, when placing the substrate G onto the spin chuck 100, a substrate G that is carried in by, e.g., a transfer arm, is placed on, e.g., elevating pins protruded through a recess (a depressed portion) 101, and then the transfer arm is retracted and the elevating pins are lowered, to load the substrate G in the recess 101. In such a loading/unloading process, direct loading of the substrate G into the recess 101 is difficult to achieve, and thus such process of loading and unloading the substrate G may become cumbersome. Furthermore, the time required in completing the series of such processes may deteriorate throughput.